The goal of this proposal is the continued immunogenetic analysis of cellular alloantigen systems of the mouse. In addition to completing studies now in progress, other studies will focus on the more recently described genes which appear to cluster at the D-end of the H-2 complex, i.e., between the S and Tla regions. Selected recombinants will be placed on a C57BL/10 genetic background and maintained as recombinant congenic strains. The strains will be used to produce more highly discriminating reagents. As in the past, congenic strains will be provided to other investigators on a cooperative and/or collaborative basis. The serological or histogenetic procedures to be used are conventional.